//-------------------------------------------------------------------
//	showidt.cpp
//
//	This application uses the '/dev/ram' device special file to 
//	read the processor's Interrupt Descriptor Table and display
//	its entries in hexadecimal format.  (The virtual address of
//	the IDT in kernel space is obtained using an "unprivileged"
//	80x86 processor instruction.) 
//
//	NOTE: Written and tested using Linux kernel version 2.4.20.
//
//	programmer: ALLAN CRUSE
//	written on: 16 MAR 2003
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <fcntl.h>	// for open() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for read(), close() 

#define N_VECTORS	256
#define TASK_SIZE	0xC0000000
#define virt_to_phys(vaddr) ( vaddr - TASK_SIZE )

char devname[] = "/dev/ram";
unsigned short idtr[3];
unsigned long idtbase, idtsize;
unsigned long long idt[ N_VECTORS ];

int main( int argc, char **argv )
{
	// open device file for reading physical memory 
	int	fd = open( devname, O_RDONLY );
	if ( fd < 0 ) { perror( "open" ); exit(1);}

	// get virtual address of the processor's IDT 
	asm(" sidt idtr " );
	idtbase = *(unsigned long*)(idtr+1);

	// read the table of interrupt descriptors
	lseek( fd, virt_to_phys(idtbase), SEEK_SET );
	int	nbytes = read( fd, idt, sizeof(idt) );
	if ( nbytes < sizeof(idt) ) { perror( "read" ); exit(1); }

	// display the descriptors in hexadecimal format
	printf( "\n\nTABLE OF INTERRUPT DESCRIPTORS %20s", " " );	
	printf( "(IDTR=%04X%04X-%04X)\n", idtr[2], idtr[1], idtr[0] );
	for (int i = 0; i < N_VECTORS; i++)
		{
		if ( ( i % 4 ) == 0 ) printf( "\n%02X: ", i );
		printf( "%016llX ", idt[ i ] );
		}
	printf( "\n\n" );	

	// close the device file
	close( fd );
}